Evaluating Rutting Resistance of Rejuvenated Recycled Hot-Mix Asphalt Mixtures Using Different Types of Recycling Agents

Growing environmental pollution worldwide is mostly caused by the accumulation of different types of liquid and solid wastes. Therefore, policies in developed countries seek to support the concept of waste recycling due to its significant impact on the environmental footprint. Hot-mix asphalt mixtures (HMA) with reclaimed asphalt pavement (RAP) have shown great performance under rutting. However, incorporating a high percentage of RAP (>25%) is a challenging issue due to the increased stiffness of the resulting mixture. The stiffness problem is resolved by employing different types of commercial and noncommercial rejuvenators. In this study, three types of noncommercial rejuvenators (waste cooking oil (WCO), waste engine oil (WEO), and date seed oil (DSO)) were used, in addition to one type of commercial rejuvenator. Three percentages of RAP (20%, 40%, and 60%) were utilized. Mixing proportions for the noncommercial additives were set as 0–10% for mixtures with 20% RAP, 12.5–17.5% for mixtures with 40% RAP, and 17.5–20% for mixtures with 60% RAP. In addition, mixing proportions for the commercial additive were set as 0.5–1.0% for mixtures with 20% RAP, 1.0–1.5% for mixtures with 40% RAP, and 1.5–2.0% for mixtures with 60% RAP. The rutting performance of the generated mixtures was indicated first by using the rutting index (G*/sin δ) for the combined binders and then evaluated using the Hamburg wheel-track test. The results showed that the rejuvenated mixtures with the commercial additive at 20 and 60% RAP performed well compared to the control mixture, whereas the rejuvenated ones at 40% RAP performed well with noncommercial additives in comparison to the control mixture. Furthermore, the optimum percentages for each type of the used additives were obtained, depending on their respective performance, as 10%, 12.5%, and 17.5% of WCO, 10%, 12.5–17.5%, and 17.5% of WEO, <10%, 12.5%, and 17.5% of DSO, and 0.5–1.0%, 1.0%, and 1.5–2.0% of the commercial rejuvenator, corresponding to the three adopted percentages of RAP.


Research Background
Pavements, especially asphaltic pavements, are reusable. The pavement's service life depends on essential factors, mainly the weight and volume of traffic, construction quality, subgrade strength, drainage system, weather, and quality of construction materials [1,2]. The service life of any pavement can be prolonged by employing timely maintenance [3,4].

Research Motivation
Sustainable development in several sectors has encouraged using waste materials as a raw material substitution. Because of the size of road networks, it is possible to employ waste from many sectors in road pavement to save money and protect the environment, which has sparked substantial studies [27,28]. Recycling agents can soften or rejuvenate the aged binder, reducing its stiffness and cracking potential by introducing some of the aged asphalt's lost components. Virgin binders can be used if the RAP binder has not deteriorated significantly [29]. As noted, pavement sustainability can be improved by including waste materials in the procedures [30].
Because of the axial force of moving cars and the large increase in traffic volume over the last several years, the service life of road pavement has greatly diminished. Hot mixture asphalts (HMA) often fail because of permanent deformation, which is typical in tropical areas. The properties of the primary components, namely bitumen and aggregates, significantly impact the performance and strength of HMA against various failures [31]. However, the current research addresses using recycled materials and finding recycled materials with low rutting stress.

Research Objectives
This study investigated three noncommercial rejuvenators (WCO, WEO, and DSO) and one commercial rejuvenator in asphaltic mixtures incorporating RAP at three levels (20%, 40%, and 60%). All the asphaltic mixtures were prepared and evaluated under the Superpave design method. In contrast, the elected aggregate gradation for preparing the mixtures is for a surface course mixed with 20%, 40%, and 60% RAP. The novelty of this study is presented by comparing the performance of commercial and noncommercial rejuvenators utilized in recycled HMA mixtures to produce a sustainable high-performance mixture capable of withstanding significant rutting stresses. All the developed Superpave mixtures are evaluated in terms of volumetric properties (air voids, voids filled with asphalt, voids of mineral aggregate) and rutting resistance using the Hamburg-wheel track test to achieve an optimal sustainable rejuvenated recycled HMA mixture with a high percentage of RAP capable of exhibiting comparable or better performance to the virgin HMA mixture.

Reclaimed Asphalt Pavement (RAP)
The RAP used in this study was collected from an old stockpile of asphalt pavement waste, as shown in Figure 1, which has been scraped for a surface layer. The gathered RAP was then crushed, screened, and stockpiled. The properties of the processed RAP are presented in Table 1. Using the AASHTO T 308 ignition method, the binder content of RAP was recovered. In contrast, the gradation of RAP was obtained according to AASHTO T 27 [23] for the recovered aggregate, as shown in Table 2.
(20%, 40%, and 60%). All the asphaltic mixtures were prepared and evaluated under Superpave design method. In contrast, the elected aggregate gradation for preparing mixtures is for a surface course mixed with 20%, 40%, and 60% RAP. The novelty of study is presented by comparing the performance of commercial and noncommercia juvenators utilized in recycled HMA mixtures to produce a sustainable high-performa mixture capable of withstanding significant rutting stresses. All the developed Superp mixtures are evaluated in terms of volumetric properties (air voids, voids filled with phalt, voids of mineral aggregate) and rutting resistance using the Hamburg-wheel tr test to achieve an optimal sustainable rejuvenated recycled HMA mixture with a h percentage of RAP capable of exhibiting comparable or better performance to the vir HMA mixture.

Reclaimed Asphalt Pavement (RAP)
The RAP used in this study was collected from an old stockpile of asphalt pavem waste, as shown in Figure 1, which has been scraped for a surface layer. The gathered R was then crushed, screened, and stockpiled. The properties of the processed RAP are p sented in Table 1. Using the AASHTO T 308 ignition method, the binder content of R was recovered. In contrast, the gradation of RAP was obtained according to AASHT 27 [23] for the recovered aggregate, as shown in Table 2.   This study used the normal crushed coarse aggregate of limestone origin from a quarry in Al-Najaf city. In contrast, the fine aggregate was brought from Karbala city; both are cities in Iraq. To achieve the Iraqi standards for coarse surface gradation (SCRB, R/9) [32], coarse and fine aggregates are sieved and then recombined in a certain ratio. The combined aggregate gradation is selected for the surface layer, as shown in Table 3. On the whole, routine tests were carried out to assess the physical features of the combined aggregate. The results and the SCRB's specified limits are summarized in Table 4.

. Asphalt Binder
Al Nasiriyah (40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50) penetration grade binder was employed. The breakdown of the binder's physical characteristics is shown in Table 5. This study used ordinary Portland cement as a filler, as in Table 6. This study used waste cooking oil gathered from residential places as a recycling agent/rejuvenator, as shown in Figure 2A. Most of the cooking oil's structure was made up of fatty acids [33]. Its physical characteristics and chemical components are presented in Tables 7 and 8.
This oil was extracted directly from the seeds of dates, as shown in Figure 2C, forming about 15% of its weight. Oleic acid is the main component of the oil, forming about 50% of its structure. Using the DSO as an efficient rejuvenator reduces such material's environmental footprint and minimizes the pavement's total cost [20]. Its physical characteristics and chemical components are presented in Tables 10 and 11.

Commercial Rejuvenator
The commercial rejuvenator used in the study was SonneWarmix RT™. It is a paraffinic wax produced by Sonneborn as an additive for asphalt mixtures. Due to its performance in terms of increasing the workability of the recycled mixture and reducing the inhalation emissions, it has been considered a promising recycling agent/rejuvenator, in addition to its compatibility with the RAP. The manufacturer's recommended dosage is 0.5-2.0% by weight of the binder [35]. A sample of SonneWarmix RT™ is shown in Figure  3, and its physical characteristics are presented in Table 12.   As shown in Figure 2B, the waste oil used for gasoline vehicles is produced mainly from paraffinic oils, with a small amount of added chemicals to enhance its viscosity, stability, cleanliness, and inflammability. As a lubricant, WEO may also comprise shortchain polar molecules that disassemble simultaneously [34]. Its physical characteristics are presented in Table 9. This oil was extracted directly from the seeds of dates, as shown in Figure 2C, forming about 15% of its weight. Oleic acid is the main component of the oil, forming about 50% of its structure. Using the DSO as an efficient rejuvenator reduces such material's environmental footprint and minimizes the pavement's total cost [20]. Its physical characteristics and chemical components are presented in Tables 10 and 11.  The commercial rejuvenator used in the study was SonneWarmix RT™. It is a paraffinic wax produced by Sonneborn as an additive for asphalt mixtures. Due to its performance in terms of increasing the workability of the recycled mixture and reducing the inhalation emissions, it has been considered a promising recycling agent/rejuvenator, in addition to its compatibility with the RAP. The manufacturer's recommended dosage is 0.5-2.0% by weight of the binder [35]. A sample of SonneWarmix RT™ is shown in Figure 3, and its physical characteristics are presented in Table 12.

Design of Asphalt Mixtures
All of the produced specimens are compacted using the Superpave gyratory compactor (SGC), as shown in Figure 4, in line with AASHTO T 312, 2015 [36] and the Superpave mix design procedure (NCHRP-752, 2013) [37].

Design of Asphalt Mixtures
All of the produced specimens are compacted using the Superpave gyrato pactor (SGC), as shown in Figure 4, in line with AASHTO T 312, 2015 [36] and the pave mix design procedure (NCHRP-752, 2013) [37].
The common compaction method is set on three different levels of gyrations Ninitial, and Nmax), where N refers to the number of gyrations used to determine th mum theoretical density of the prepared specimens. Medium to high traffic leve used to select the Ndesign at 100 gyrations from NCHRP-714, 2012 [38]. The level paction sets from SHRP-A-407 [39] suits Babylon's city climate and traffic in shown in Table 13.  After selecting the aggregate design structure, a trial mixture was conducted mate the binder content based on the Asphalt Institute Manual, 2014. Normally binder content was used depending on the nominal maximum size of the ag The common compaction method is set on three different levels of gyrations (N design , N initial , and N max ), where N refers to the number of gyrations used to determine the maximum theoretical density of the prepared specimens. Medium to high traffic levels were used to select the N design at 100 gyrations from NCHRP-714, 2012 [38]. The level of compaction sets from SHRP-A-407 [39] suits Babylon's city climate and traffic in Iraq, as shown in Table 13. After selecting the aggregate design structure, a trial mixture was conducted to estimate the binder content based on the Asphalt Institute Manual, 2014. Normally, a trial binder content was used depending on the nominal maximum size of the aggregate, which is 12.5 mm for the surface layer. In our case, the elected content equals 5%, depending on the design procedure of the Asphalt Institute. This procedure aims to calculate the amount of binder required to achieve 4% air content in the compacted mixes. In order to conduct the maximum theoretical and bulk-specific gravity (Gmm and Gmb) in line with AASHTO T 209 [40] and AASHTO T 166 [41], respectively, Superpave specimens were compacted using 4790 gm at the chosen binder content for trial. At 5% binder, the trial mixture's air content deviated from 4% or 96% Gmm. Therefore, after multiple trials, the target has reached an estimated 4.9% binder content, which corresponds to the desired air content. All related design equations for predicting binder content were applied following AASHTO R 35 [42]. The volumetric properties of trial mixtures at estimated binder content are presented in Table 14. As a result of compacting four different types of mixtures, each has a certain amount of binder; as listed below, the optimum binder content is identified. Three asphalt specimens have been compacted for each binder percent.

•
The first trial mixture is mixed at the estimated content of the binder; • The second trial mixture is mixed at the estimated content of the binder minus 0.5%; • The third trial mixture is mixed at the estimated content of binder plus 0.5%; • The fourth trial mixture is mixed at the estimated content of binder plus 1.0%.
The volumetric properties of the developed mixtures are obtained by considering air voids, VFA, and VMA and the value of Gmm at each gyration level (NCHRP-673, 2011) [44]. The optimum binder content is fixed at 4% air content, consistent with AASHTO R 35.
AASHTO M 323 [43] is used as the basis for handling the RAP in the HMA mixtures. Choosing the proper grade of virgin binder depends on the viscosity and penetration of the recovered RAP binder; hence, special blending charts are needed only for mixes having a high percentage of RAP, more than 25%.
The combined blend between the fresh binder and the aged RAP binder is dense, with high viscosity, and is made denser by increasing the percentage of RAP within the mixture. Therefore, a radical solution is needed by providing a softer virgin binder or adopting recycling agents/rejuvenators to mix with the recycled mixtures. Recovering basic characteristics of the aged binder within the old pavement is implemented using different viscous oils. The whole process can be summarized by adding new maltenes to dilute the asphaltenes that have formed due to time.
The amount of virgin binder that can be added to the recycled HMA mixture depends on the amount of RAP in the mix; therefore, the Asphalt Institute and AASHTO M 323 developed an equation to calculate the added percentage of fresh binder [45].
where P R is the percentage of virgin binder in the mix, P A is the percentage of RAP binder, P C is the total binder content in the mix, and P P is the percentage of RAP in the mix.

Rolling Thin Film Oven Test Aging (RTFO)
The RTFO test is performed to change the binders' condition from unaged to shortterm aged by following the AASHTO T 240 test method [46]. The apparatus and an RTFO bottle are shown in Figure 5. It stimulates the binder's aging during manufacturing and placement in the field. The RTFO chamber was preheated at 163 • C. Subsequently, the sample bottles, after cooling down, were carefully put into a carousel oven. The carousel rotates at a constant speed of 15 RPM for 85 min. Throughout the rotation of the carousel, the temperature of the oven and the airflow rate into bottles were maintained at 163 • C and 4 lit/min, respectively. The RTFO residue was tested within 72 h. term aged by following the AASHTO T 240 test method [46]. The apparatus and an RTFO bottle are shown in Figure 5. It stimulates the binder's aging during manufacturing and placement in the field. The RTFO chamber was preheated at 163°C. Subsequently, the sample bottles, after cooling down, were carefully put into a carousel oven. The carousel rotates at a constant speed of 15 RPM for 85 min. Throughout the rotation of the carousel, the temperature of the oven and the airflow rate into bottles were maintained at 163°C and 4 lit/min, respectively. The RTFO residue was tested within 72 h.

Measuring the Viscosity
Viscosity for the modified and unmodified asphalt binders is usually determined by using a rotational Brookfield viscometer, as shown in Figure 6, through the traditional standard method ((ASTM D4402) [47]/(AASHTO T316) [48]). The rotational Brookfield (RV) test is performed at constant rotational speed (20 RPM) of a cylindrical spindle while submerged in a binder. The amount of binder used varies with the spindle size, at most 11 gm. Viscosity values were obtained for the unmodified binders at pumping and handling temperatures to prepare the logarithm of viscosity versus the logarithm of temperature charts for the unmodified binder, as shown in Figure 7, that can be used to determine equiviscous mixing and compaction temperatures corresponding to viscosity ranges of 0.17 ± 0.02 Pa.s and 0.28 ± 0.03 Pa.s, respectively. Consequently, the viscosity values were measured at 135 °C and 165 °C, then a straight line was drawn to connect these two points.
Several trials of the modified combined blend (the recovered aged binder of RAP + rejuvenators) were conducted at each percent of RAP within the HMA mixtures using the rotational Brookfield viscometer. The aim of the trials is to determine the potential effect of the rejuvenators by achieving a considerable level of viscosity similar to or close enough to the level of the control virgin binder. The adopted percentages of the recycling agents are illustrated in Table 15.

Measuring the Viscosity
Viscosity for the modified and unmodified asphalt binders is usually determined by using a rotational Brookfield viscometer, as shown in Figure 6, through the traditional standard method ((ASTM D4402) [47]/(AASHTO T316) [48]). The rotational Brookfield (RV) test is performed at constant rotational speed (20 RPM) of a cylindrical spindle while submerged in a binder. The amount of binder used varies with the spindle size, at most 11 gm. Viscosity values were obtained for the unmodified binders at pumping and handling temperatures to prepare the logarithm of viscosity versus the logarithm of temperature charts for the unmodified binder, as shown in Figure 7, that can be used to determine equiviscous mixing and compaction temperatures corresponding to viscosity ranges of 0.17 ± 0.02 Pa.s and 0.28 ± 0.03 Pa.s, respectively. Consequently, the viscosity values were measured at 135 • C and 165 • C, then a straight line was drawn to connect these two points.
The used additive by weight of aged RAP binder = additive% × (% of aged binder by weight of total mix × total binder weight in the mix).

Dynamic Shear Rheometer
A DSR test was performed to evaluate the effect of different types of rejuvenators within the recycled HMA on the rheological properties by determining the complex modulus and phase angle at high temperatures under torques ranging from 0.5 μN·m to 200 Several trials of the modified combined blend (the recovered aged binder of RAP + rejuvenators) were conducted at each percent of RAP within the HMA mixtures using the rotational Brookfield viscometer. The aim of the trials is to determine the potential effect of the rejuvenators by achieving a considerable level of viscosity similar to or close enough to the level of the control virgin binder. The adopted percentages of the recycling agents are illustrated in Table 15. * The used additive by weight of aged RAP binder = additive% × (% of aged binder by weight of total mix × total binder weight in the mix).

Dynamic Shear Rheometer
A DSR test was performed to evaluate the effect of different types of rejuvenators within the recycled HMA on the rheological properties by determining the complex modulus and phase angle at high temperatures under torques ranging from 0.5 µN·m to 200 µN·m according to AASHTO T315 [49]. The DSR works by converting applied torque to strain while the sample is saved in an active hood (thermally controlled test chamber) throughout testing to accurately and dependably manage the temperature within ±0.1 • C tolerance. When testing unaged and RTFO binders at high temperatures, the (G*/sin δ) value is employed as the rutting index. According to a general rule, a larger (G*/sin δ) indicates a high permanent deformation confrontation. Kinexus DSR from Malvern Instruments was utilized in this test, as shown in Figure 8.
μN·m according to AASHTO T315 [49]. The DSR works by converting applied torque to strain while the sample is saved in an active hood (thermally controlled test chamber) throughout testing to accurately and dependably manage the temperature within ±0.1 °C tolerance. When testing unaged and RTFO binders at high temperatures, the (G*/sin δ) value is employed as the rutting index. According to a general rule, a larger (G*/sin δ) indicates a high permanent deformation confrontation. Kinexus DSR from Malvern Instruments was utilized in this test, as shown in Figure 8.

Hamburg Wheel-Track Test
In line with AASHTO T-324 [50], the wheel tracking test (WTT) was applied to simulate the rutting susceptibility of laboratory-prepared asphalt mixtures to deform under load, as shown in Figure 9. The permanent deformations (rut depth) produced by repeated wheel load cycles at a certain temperature were simulated using the WTT. A rubber wheel that is 203.2 mm in diameter and 47 mm wide can be moved across a test specimen using the mechanical wheel tracking mechanism. The table of the device has an alternate harmonic spanning a distance of 230 ± 5 mm at 52 RPM with the wheel in one forward and backward motion (two passes), which is considered one load cycle.
The wheel has a solid rubber tire with a diameter of 200 mm and a maximum speed of roughly 0.305 m/s. The standard wheel load is 700 ± 10 N while the wheel tracker is located in temperature-controlled cabinets up to 65 ± 1.0 °C and is designed to capture at least two readings at 25 places along a 10 cm line at the center of the sample immediately along the wheel route. The WTT temperature was set at 60°C for this study to represent the most extreme high-performance temperature in hot locations. The WTT test is completed when the wheel has completed 10,000 revolutions over the specimen or when the rut depth exceeds 20 mm.

Hamburg Wheel-Track Test
In line with AASHTO T-324 [50], the wheel tracking test (WTT) was applied to simulate the rutting susceptibility of laboratory-prepared asphalt mixtures to deform under load, as shown in Figure 9. The permanent deformations (rut depth) produced by repeated wheel load cycles at a certain temperature were simulated using the WTT. A rubber wheel that is 203.2 mm in diameter and 47 mm wide can be moved across a test specimen using the mechanical wheel tracking mechanism. The table of the device has an alternate harmonic spanning a distance of 230 ± 5 mm at 52 RPM with the wheel in one forward and backward motion (two passes), which is considered one load cycle. Preparation Process of the Samples A pneumatic roller compactor, as shown in Figure 10, was used to compact a slab sample in a rectangular mold, as shown in Figure 11, of 400 mm × 300 mm × 120 mm. With a batch of 11 kg, two slab samples were implemented for each type of the adopted mixture to generate samples with a thickness of 40 mm (thickness must be at least twice the nom- The wheel has a solid rubber tire with a diameter of 200 mm and a maximum speed of roughly 0.305 m/s. The standard wheel load is 700 ± 10 N while the wheel tracker is located in temperature-controlled cabinets up to 65 ± 1.0 • C and is designed to capture at least two readings at 25 places along a 10 cm line at the center of the sample immediately along the wheel route. The WTT temperature was set at 60 • C for this study to represent the most extreme high-performance temperature in hot locations. The WTT test is completed when the wheel has completed 10,000 revolutions over the specimen or when the rut depth exceeds 20 mm.

Preparation Process of the Samples
A pneumatic roller compactor, as shown in Figure 10, was used to compact a slab sample in a rectangular mold, as shown in Figure 11, of 400 mm × 300 mm × 120 mm. With a batch of 11 kg, two slab samples were implemented for each type of the adopted mixture to generate samples with a thickness of 40 mm (thickness must be at least twice the nominal aggregate maximum size) (EN 12697-22) [51]. Before applying the test, each compacted slab's air void was examined. If the air void exceeded 4% ± 0.5%, the compacted slab was disposed of and replaced. AASHTO R 30 [52] required that HMA samples be conditioned for 4 h at 135 • C. Preparation Process of the Samples A pneumatic roller compactor, as shown in Figure 10, was used to c sample in a rectangular mold, as shown in Figure 11, of 400 mm × 300 mm × a batch of 11 kg, two slab samples were implemented for each type of the ad to generate samples with a thickness of 40 mm (thickness must be at least t inal aggregate maximum size) (EN 12697-22) [51]. Before applying the te pacted slab's air void was examined. If the air void exceeded 4% ± 0.5%, t slab was disposed of and replaced. AASHTO R 30 [52] required that HM conditioned for 4 h at 135 °C.

Results and Discussion
The optimum binder content for the designed HMA mixtures is pred content. The rest of the volumetric properties-VFA, VMA, and the level of Ndesign, and Ninitial-have been figured out in line with NCHRP-673, 2011 [53

Results and Discussion
The optimum binder content for the designed HMA mixtures is predicted at 4% air content. The rest of the volumetric properties-VFA, VMA, and the level of Gmm at N max , N design , and N initial -have been figured out in line with NCHRP-673, 2011 [53], as shown in Table 16 and Figure 12.  The added percentage of fresh or virgin binder to the recycled HMA mixtures at each percent of RAP is tabulated in Table 18. * The % of aged binder by weight of of total binder conctent = % of aged binder by weight of total mix divided by the % of The optimum content of the binder is 4.8%, determined at 4% air voids in line with AASHTO M 323 for Superpave mix design. The volumetric properties of the generated specimens at the optimum binder content are illustrated in Table 17. The added percentage of fresh or virgin binder to the recycled HMA mixtures at each percent of RAP is tabulated in Table 18. * The % of aged binder by weight of of total binder conctent = % of aged binder by weight of total mix divided by the % of total binder content.

Blending Process of the Rejuvenators and the Virgin Binder
The added quantities of WCO, WEO, and DSO are calculated by the weight of the aged RAP binder in the recycled mix, whereas it depends mainly on the percentage of RAP within the mix. In contrast, the added dosage of SonneWarmix RT TM is calculated by the weight of the total binder in the mix. The mixing process is a wet process in which the rejuvenators are added to the asphalt binder before introducing it into the asphalt concrete mixture. All the used rejuvenators are added to the asphalt binder in a blending machine at a blending speed of 600 RPM for half an hour at 160 • C [53], as shown in Figure 13.

Measuring the Variation in Viscosity of the Aged Blend of Binders Due to Adding the Used Rejuvenators
The effects of the rejuvenators on the viscosity levels of the combined blend of binders (aged + virgin) are demonstrated in Figures 14-16.

Measuring the Variation in Viscosity of the Aged Blend of Binders Due to Adding the Used Rejuvenators
The effects of the rejuvenators on the viscosity levels of the combined blend of binders (aged + virgin) are demonstrated in Figures 14-16.

Measuring the Variation in Viscosity of the Aged Blend of Binders Due to Adding the Used Rejuvenators
The effects of the rejuvenators on the viscosity levels of the combined blend of binders (aged + virgin) are demonstrated in Figures 14-16.       Depending on the added percentages of RAP within the recycled mixtures, the effects of the rejuvenators on the viscosity behavior are presented.

Combined Blend of (Aged + Virgin) Binder + WCO
Adding WCO to the aged blend of binders affected the viscosity of the blend, as demonstrated in Figure 17. WCO tries to push the aged blend to regain the physical characteristics that were lost due to aging by enhancing its molecular structures and makes it  Depending on the added percentages of RAP within the recycled mixtures, the effects of the rejuvenators on the viscosity behavior are presented.

Combined Blend of (Aged + Virgin) Binder + WCO
Adding WCO to the aged blend of binders affected the viscosity of the blend, as demonstrated in Figure 17. WCO tries to push the aged blend to regain the physical characteristics that were lost due to aging by enhancing its molecular structures and makes it similar in performance to the virgin binder. In other words, WCO has cured the hard and stiff aging defects in the aged blend of binders. By comparing this result with the findings of Dokandari et al. [54], a similarity in the methodology is noticed, but the current study offers new parameters and evaluation tests to continue the prior study. Both percentages of RAP-binder and WCO within the blend significantly affect the viscosity values; therefore, at high percentage of RAP (>25%), two percentages of WCO have been mixed with each percent of RAP in order to reach the optimum content of the used rejuvenator that could rejuvenate the aged blend effectively.  [54], a similarity in the methodology is noticed, but the current study offers new parameters and evaluation tests to continue the prior study. Both percentages of RAP-binder and WCO within the blend significantly affect the viscosity values; therefore, at high percentage of RAP (>25%), two percentages of WCO have been mixed with each percent of RAP in order to reach the optimum content of the used rejuvenator that could rejuvenate the aged blend effectively.  Figure 18. The unique structure of WEO works to enhance the structures of the aged binder at a molecular level with sufficient aromatic content, which results in 2

Combined Blend of (Aged + Virgin) Binder + WEO
Adding WEO to the aged blend of binders affected the viscosity of the blend, as demonstrated in Figure 18. The unique structure of WEO works to enhance the structures of the aged binder at a molecular level with sufficient aromatic content, which results in cohesive bonding through modifying the aged binder components and rejuvenating the lost physical and chemical characteristics. This result is supported by the findings of Woszuk et al. [55], in addition to adding new boundary conditions in terms of mixing and compaction temperatures to develop the previous work. The optimal content of the utilized rejuvenator that could revive the aged blend, especially at high RAP content (>25%), was determined by mixing two percentages of WEO with each percent of RAP.

Combined Blend of (Aged + Virgin) Binder + WEO
Adding WEO to the aged blend of binders affected the viscosity of the blend, as demonstrated in Figure 18. The unique structure of WEO works to enhance the structures of the aged binder at a molecular level with sufficient aromatic content, which results in cohesive bonding through modifying the aged binder components and rejuvenating the lost physical and chemical characteristics. This result is supported by the findings of Woszuk et al. [55], in addition to adding new boundary conditions in terms of mixing and compaction temperatures to develop the previous work. The optimal content of the utilized rejuvenator that could revive the aged blend, especially at high RAP content (> 25%), was determined by mixing two percentages of WEO with each percent of RAP.

Combined Blend of (Aged + Virgin) Binder + DSO
Adding DSO to the aged blend of binders affected the viscosity of the blend, as demonstrated in Figure 19. DSO consists of fatty acids, which are long aliphatic chains of carboxylic acids with the ability to restore the original properties of the aged binder as a rejuvenator. This result ties well with the results gained by Mirhosseini AF. et al. [19]. In addition, the current study utilized several DSO proportions that were mixed with each percent of RAP in order to conduct the optimal rejuvenator content as a step of development.  Figure 19. DSO consists of fatty acids, which are long aliphatic chains of carboxylic acids with the ability to restore the original properties of the aged binder as a rejuvenator. This result ties well with the results gained by Mirhosseini AF. et al. [19]. In addition, the current study utilized several DSO proportions that were mixed with each percent of RAP in order to conduct the optimal rejuvenator content as a step of development.  Figure 20. SonneWarmix RT TM reduces the damage caused by 5

Combined Blend of (Aged + Virgin) Binder + SonneWarmix RT TM
Adding SonneWarmix RT TM to the aged blend of binders affected the viscosity of the blend, as demonstrated in Figure 20. SonneWarmix RT TM reduces the damage caused by oxidative aging of binder and tries to regain the lost properties. Overall, the current findings are in accordance with findings reported by Zinke S. et al. [29], wherein new performance tests have been implemented to continue the previous work.

Combined Blend of (Aged + Virgin) Binder + SonneWarmix RT TM
Adding SonneWarmix RT TM to the aged blend of binders affected the viscosity of the blend, as demonstrated in Figure 20. SonneWarmix RT TM reduces the damage caused by oxidative aging of binder and tries to regain the lost properties. Overall, the current findings are in accordance with findings reported by Zinke S. et al. [29], wherein new performance tests have been implemented to continue the previous work.   In terms of viscosity enhancement of aged binders compared to the control, at 20% RAP, the performance of noncommercial rejuvenators was better than the commercial ones for all the adopted percentages at 135 • C, whereas at 165 • C, best results were achieved using either 10% WEO or 0.5% SonneWarmix RT TM , which have the same effect on the viscosity level.
At 40% RAP, using 12.5% and 1.0% of the noncommercial and commercial rejuvenators, respectively, the viscosity level was modified better using the noncommercial rejuvenators at both 135 • C and 165 • C, in comparison to the control binder. Increasing the rejuvenator percentages to 17.5% and 1.5% at 40% RAP for both types, respectively, led to effectively improving the viscosity of the aged binder by the commercial rejuvenator at 135 • C, whereas at 165 • C, the best result was achieved using the DSO rejuvenator in comparison to the control binder.
Furthermore, at 60% RAP, using 17.5% and 1.5% of the noncommercial and commercial rejuvenators, respectively, the viscosity level was modified better using the noncommercial rejuvenators at both 135 • C and 165 • C in comparison to the control binder. In addition, increasing the rejuvenator percentages to 20% and 2.0% at 60% RAP for both types, respectively, led to the best result using the WEO rejuvenator at 135 • C, whereas at 165 • C, the best result was achieved using the commercial rejuvenator in comparison to the control binder.
Increasing and decreasing the levels of viscosity of the combined blend of binders after mixing with the rejuvenators, as presented in Figures 19-22, can be interpreted depending on the percentage of the aged binder within the blend. As high as the percentage of aged binder, a high percentage of the rejuvenator is required to equalize the stiffness of the blend, and vice versa.
12.5% WCO and 60% RAP + 17.5% WCO, whereas the levels of G*/sin δ for the noted blends of binders are relatively high in comparison to the virgin ones, which indicates high resistance to rutting deformation. WCO has motivated the aged blend to restore the physical qualities lost due to aging by improving its molecular structure and making it similar to the virgin binder. The current results are directly in line with prior findings of Dokandari et al. [54]. In addition, it adds new testing parameters to the previous ones. Figure 21. Rutting index (G*/sin δ) for the aged blends of binders rejuvenated by WCO.

Using WEO within the aged blend of binders has proven to be very reliable in stabi-
lizing the rutting index (G*/sin δ) equally with the control virgin binder, as shown in Figure 22. Best results were achieved by the rejuvenated blends of 20% RAP + 10% WEO, 40% RAP + 12.5% WEO, 40% RAP + 17.5% WEO, and 60% RAP + 17.5% WEO, whereas levels of G*/sin δ for the noted blends of binders are higher or similar to the level of virgin binder, which indicates high resistance to rutting deformation. Through the modification of the old binder components and restoration of the lost physical and chemical properties, the distinctive WEO structure works to improve the aged binder's molecular structures and provide cohesive bonding. Woszuk et al. [55] support these outcomes using the same testing procedure at only two degrees of test temperatures.  3. Using DSO within the aged blend of binders has proven to be very effective in stabilizing the rutting index (G*/sin δ) equally with the control virgin binder, as shown in Figure 23. A high level of rutting index was achieved by the rejuvenated blends of 40% RAP + 12.5% DSO and 60% RAP + 17.5% DSO, which indicates a high resistance to rutting deformation. Fatty acids, which are long aliphatic chains of carboxylic acids and are part of DSO composition, have the power to revive the aged binder in terms of physical and chemical properties. These results are consistent with the findings of Mirhosseini AF. et al. [19].   Therefore, two individual percentages of the used rejuvenators were used at each percent of RAP, as previously shown in Table 15. In addition, it also depends on the characteristics of the rejuvenators used. This result is supported by the findings of Zaumanis et al. [56], wherein new mixing parameters are presented in the current research to continue the prior study.

Rutting Potential Indicator (G*/sin δ) for Binders
According to AASHTO T315, the DSR test was implemented to predict the effect of the used rejuvenators on the rheological characteristics of the combined blend of binders, as shown in Tables 19 and 20. The effects of rejuvenators on the rutting index (G*/sin δ) can be explained due to changing the viscosity of the combined blends of binders, whereas the rejuvenators work to enhance the characteristics of the aged binder and minimize its hard viscosity. In other words, the rejuvenators change the performance grade (PG) of the aged blend and make it similar to the virgin one. A similar pattern of results was obtained previously by Shen et al. [47], except the current study offers a variety in the used rejuvenators under different circumstances. The effects of adding recycling agents/rejuvenators on the levels of rutting index (G*/sin δ) for the aged blend of binders are demonstrated below for the unaged and aged samples of binders.

1.
Using WCO within the aged blend of binders has proven to be very efficient in stabilizing the rutting index (G*/sin δ) equally with the control virgin binder, as shown in Figure 21. Best results were achieved by the rejuvenated blends of 40% RAP + 12.5% WCO and 60% RAP + 17.5% WCO, whereas the levels of G*/sin δ for the noted blends of binders are relatively high in comparison to the virgin ones, which indicates high resistance to rutting deformation. WCO has motivated the aged blend to restore the physical qualities lost due to aging by improving its molecular structure and making it similar to the virgin binder. The current results are directly in line with prior findings of Dokandari et al. [54]. In addition, it adds new testing parameters to the previous ones.

2.
Using WEO within the aged blend of binders has proven to be very reliable in stabilizing the rutting index (G*/sin δ) equally with the control virgin binder, as shown in Figure 22. Best results were achieved by the rejuvenated blends of 20% RAP + 10% WEO, 40% RAP + 12.5% WEO, 40% RAP + 17.5% WEO, and 60% RAP + 17.5% WEO, whereas levels of G*/sin δ for the noted blends of binders are higher or similar to the level of virgin binder, which indicates high resistance to rutting deformation. Through the modification of the old binder components and restoration of the lost physical and chemical properties, the distinctive WEO structure works to improve the aged binder's molecular structures and provide cohesive bonding.
Woszuk et al. [55] support these outcomes using the same testing procedure at only two degrees of test temperatures. 3.
Using DSO within the aged blend of binders has proven to be very effective in stabilizing the rutting index (G*/sin δ) equally with the control virgin binder, as shown in Figure 23. A high level of rutting index was achieved by the rejuvenated blends of 40% RAP + 12.5% DSO and 60% RAP + 17.5% DSO, which indicates a high resistance to rutting deformation. Fatty acids, which are long aliphatic chains of carboxylic acids and are part of DSO composition, have the power to revive the aged binder in terms of physical and chemical properties. These results are consistent with the findings of Mirhosseini AF. et al. [19]. 4.
Using SonneWarmix RT TM within the aged blend of binders has proven to be very efficient in stabilizing the rutting index (G*/sin δ) equally with the control virgin binder, as shown in Figure 24. A high level of rutting index was achieved by almost all of the developed binder blends similar to or higher than the level of control binder, except the blend of 40% RAP + 1.5% SonneWarmix RT TM , which has a relatively low value of rutting index. SonneWarmix RT TM mitigates binder oxidative aging damage and attempts to restore lost characteristics. The current results are consistent with those reported by Zinke S. et al. [29], although they used different percentages of SonneWarmix RT TM and a different testing approach. lizing the rutting index (G*/sin δ) equally with the control virgin binder, as shown in Figure 23. A high level of rutting index was achieved by the rejuvenated blends of 40% RAP + 12.5% DSO and 60% RAP + 17.5% DSO, which indicates a high resistance to rutting deformation. Fatty acids, which are long aliphatic chains of carboxylic acids and are part of DSO composition, have the power to revive the aged binder in terms of physical and chemical properties. These results are consistent with the findings of Mirhosseini AF. et al. [19]. 4. Using SonneWarmix RT TM within the aged blend of binders has proven to be very efficient in stabilizing the rutting index (G*/sin δ) equally with the control virgin binder, as shown in Figure 24. A high level of rutting index was achieved by almost all of the developed binder blends similar to or higher than the level of control binder, except the blend of 40% RAP + 1.5% SonneWarmix RT TM , which has a relatively low value of rutting index. SonneWarmix RT TM mitigates binder oxidative aging damage and attempts to restore lost characteristics. The current results are consistent with those reported by Zinke S. et al. [29], although they used different percentages of SonneWarmix RT TM and a different testing approach.  Regarding rutting index (G*/sin) modification of the unaged and RTFO-aged binders, the performance of the commercial rejuvenator at 20% RAP was better than noncommercial ones at all the adopted percentages under 64 °C, 70 °C, and 76 °C test temperatures compared to the control level. At 40% RAP, the performance of the noncommercial rejuvenator was better than the commercial ones at all the adopted percentages under 64 °C, 70 °C, and 76 °C test temperatures in comparison to the control level. At 60% RAP, the performance of the commercial rejuvenator at 20% RAP was better than noncommercial ones at all the adopted percentages under 64 °C, 70 °C, and 76 °C test temperatures compared to the control level.
The effect of the rejuvenators on the rutting index (G*/sin δ) of the aged binder can be explained by enhancing the aged characteristics of the binder and changing its PG to be similar to the virgin one or even better, leading to generating recycled mixtures with significant resistance to rutting stresses.
In addition, each type of the used rejuvenators has its effect in enhancing the rutting index (G*/sin δ) depending on its characteristics and the recommended mixing dosage. This result ties well with the prior study implemented by Al-Saffar et al. [19].  Regarding rutting index (G*/sin) modification of the unaged and RTFO-aged binders, the performance of the commercial rejuvenator at 20% RAP was better than noncommercial ones at all the adopted percentages under 64 • C, 70 • C, and 76 • C test temperatures compared to the control level. At 40% RAP, the performance of the noncommercial rejuvenator was better than the commercial ones at all the adopted percentages under 64 • C, 70 • C, and 76 • C test temperatures in comparison to the control level. At 60% RAP, the performance of the commercial rejuvenator at 20% RAP was better than noncommercial ones at all the adopted percentages under 64 • C, 70 • C, and 76 • C test temperatures compared to the control level.

The Results of WTT
The effect of the rejuvenators on the rutting index (G*/sin δ) of the aged binder can be explained by enhancing the aged characteristics of the binder and changing its PG to be similar to the virgin one or even better, leading to generating recycled mixtures with significant resistance to rutting stresses.
In addition, each type of the used rejuvenators has its effect in enhancing the rutting index (G*/sin δ) depending on its characteristics and the recommended mixing dosage. This result ties well with the prior study implemented by Al-Saffar et al. [19]. All the related results for the Hamburg test are demonstrated in Table 21, considering all the effects of the variation in binder grade at each type and percentage of the used rejuvenators. It is worth noting that the obtained rut depth for 10,000 cycles was 11.7 mm when the 40% of HMA RAP +1.5 SonneWarmix RT TM , whereas the resulting depth of 60% of HMA RAP +1.5 SonneWarmix RT TM was noted as 7.6 mm. This can be explained due to the rigidity properties of the 60% mixture that behave in this manner under rutting, in comparison with the control mixture. The most reliable interpretation for the results of WTT is listed below for each case:

The Results of WTT
i.
As shown in Figure 25, HMA mixtures of RAP + WCO showed noticeable levels of rutting resistance in comparison to the control mixture. The mixtures that accomplished the best performance under rutting were 40% RAP + 12.5% WCO and 60% RAP + 17.5% WCO. ii.
As shown in Figure 27, HMA mixtures of RAP + DSO showed great levels of rutting resistance in comparison to the control mixture. Moreover, mixtures that accomplished the best performance under rutting were 40% RAP + 12.5% DSO and 60% RAP + 17.5% DSO. iv.
As shown in Figure 28, HMA mixtures of RAP + SonneWarmix RT TM showed remarkable levels of rutting resistance in comparison to the control mixtures. All the rejuvenated mixtures using SonneWarmix RT TM accomplished the best performance under rutting, except the HMA mixture of 40% RAP + 1.5% SonneWarmix RT TM , which showed a low level of rutting resistance in comparison to the control mixture. mercial and noncommercial rejuvenators within the recycled HMA mixtures were determined in terms of equalizing the aged characteristics of the combined blends of binders and enhancing the rutting resistance, as shown in Table 22.    mercial and noncommercial rejuvenators within the recycled HMA mixtures were determined in terms of equalizing the aged characteristics of the combined blends of binders and enhancing the rutting resistance, as shown in Table 22.

Conclusions
In this research, three noncommercial rejuvenators (i.e., WCO, WEO, and DSO) and one commercial rejuvenator in asphaltic mixtures incorporating RAP at three levels (20%, 40%, and 60%), were investigated. All the asphaltic mixtures were prepared and evaluated under the Superpave design method. The elected aggregate gradation for preparing the

Conclusions
In this research, three noncommercial rejuvenators (i.e., WCO, WEO, and DSO) and one commercial rejuvenator in asphaltic mixtures incorporating RAP at three levels (20%, 40%, and 60%), were investigated. All the asphaltic mixtures were prepared and evaluated under the Superpave design method. The elected aggregate gradation for preparing the Overall, the performance of rejuvenated HMA mixtures under rutting was implemented by using both rejuvenator types. At 20% RAP, the performance of the commercial rejuvenator at all the conducted percentages proved to be very effective in reducing the rutting depth in comparison to the control mix under all test cycles. At 40% RAP, the performance of noncommercial rejuvenators at all the conducted percentages proved to be very effective in reducing the rutting depth in comparison to the control mix under all test cycles. At 60% RAP, the performance of the commercial rejuvenator at all the conducted percentages proved to be very effective in reducing the rutting depth in comparison to the control mix under all test cycles (Table 22). The optimum percentages of the used commercial and noncommercial rejuvenators within the recycled HMA mixtures were determined in terms of equalizing the aged characteristics of the combined blends of binders and enhancing the rutting resistance, as shown in Table 22.

Conclusions
In this research, three noncommercial rejuvenators (i.e., WCO, WEO, and DSO) and one commercial rejuvenator in asphaltic mixtures incorporating RAP at three levels (20%, 40%, and 60%), were investigated. All the asphaltic mixtures were prepared and evaluated under the Superpave design method. The elected aggregate gradation for preparing the mixtures was for surface course mixed with 20%, 40%, and 60% RAP. The conclusions of this research are summarized as follows: i.
The optimum percentages of the used noncommercial rejuvenators (i.e., 20% RAP) were within the recycled HMA mixtures. whereas for the commercial rejuvenator (i.e., 0.5-1.0% SonneWarmix RT TM ) it was determined by the total weight of binder content. ii.
All the obtained results of the rutting tests of the rejuvenated recycled mixtures were confirmed by the achieved results using rutting index (G*/sin δ) with respect to the rejuvenated blends of binders. iii.
The best resistance to rutting stresses was accomplished at 20 and 60% RAP by the rejuvenated recycled HMA mixtures using SonneWarmix RT TM , whereas the best rutting resistance at 40% RAP was accomplished by the rejuvenated recycled mixtures using all three types of noncommercial additives (i.e., WCO, WEO, and DSO) in comparison to the control mixture. iv.
All the rejuvenated binders proved to be stiff and elastic with the ability to regain their shapes after removing the deformation. This research accomplished that by using the optimal dosages of commercial and noncommercial rejuvenators. v.
All the used rejuvenators performed very well in minimizing the high viscosity of the combined aged blends of binders to acceptable levels, in comparison to the control viscosity of virgin binders. vi.
The working mechanism of the adopted rejuvenators involved changing the performance grade (PG) of the aged binder to a softer grade similar to that of the control virgin binder.
The current study contributes to the previous findings of researchers by conducting a comprehensive investigation using two types of recycling agents with affordable prices to rejuvenate recycled HMA mixtures and trying to compare the performance of each type of rejuvenator in terms of rutting resistance. Despite that, one of the limitations of this study is the lack of some tests for the used asphalt binder, including binder pressure aging vessel (PAV) and frequency sweep test (FST). Thus, it is recommended for future work to implement an extensive investigation regarding the aforementioned tests to overcome this limitation.